Hour Timers

100 Hour Timer

Reliable 100 hour countdown timer with background tab precision and alarm sound.

100:00:00

Press Space to start or pause · ? for shortcuts

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Keyboard shortcuts

Space
Start / pause
R
Reset
+
Add 1 minute
E
Edit time
F
Fullscreen
M
Mute / unmute
Esc
Stop alarm / exit fullscreen
?
Show shortcuts

100 Hour Timer with Alarm

A 100 hour countdown that keeps accurate time even when the tab is in the background. Leave it open, carry on with your day, and a chime will tell you when time is up.

Need to set a timer for 100 hours? This one is ready to go. It's already set to 100:00:00, so all you have to do is press Start. You don't need to type anything in, install an app or create an account.

As it counts down, the ring around the clock gets shorter so you can see the time left without reading the numbers. The countdown also shows in your browser tab, so you can work in another tab and still see it. When it reaches zero, a chime plays. Check that your sound is on.

People use a 100 hour timer for things like fasting windows, slow-cooked recipes, long bakes, charging cycles, or tracking a long task over the day.

Duration
100 hours (100:00:00)
In seconds
360,000 seconds
Alarm
Chime at 00:00

Frequently Asked Questions

How many seconds are in 100 hours?

100 hours is 360,000 seconds. The timer shows it as 100:00:00 when it starts.

Will the alarm still go off if I switch tabs?

Yes. The timer goes by your device's clock, so it doesn't slow down when the browser puts the tab in the background. Keep the tab open and your volume up. On some phones the browser can't play sound while the screen is locked, so it's safer to keep the screen on.

Can I change the time or make it fullscreen?

Yes. Tap Edit to set any hours, minutes and seconds you like, or tap Fullscreen to show a big countdown on a classroom board, TV or kitchen tablet.

What is a 100 hour timer good for?

100 hours works well for fasting windows, slow-cooked recipes, long bakes, charging cycles, or tracking a long task over the day. Very long timers need the tab to stay open the whole time. Turn off sleep mode or keep the device on a charger.

Can I share this timer or put it on my website?

Yes. Tap Share to copy a link (it includes any custom time you set), or copy a short code that embeds the timer on your own website or classroom page.

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